KVM: arm64: Clarify vcpu reset behaviour

Although the KVM_ARM_VCPU_INIT documentation mention that the
registers are reset to their "initial values", it doesn't
describe what these values are.

Describe this state explicitly.

Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>

Documentation/virt/kvm/api.rst

@@ -3115,6 +3115,18 @@ optional features it should have.  This will cause a reset of the cpu
 registers to their initial values.  If this is not called, KVM_RUN will
 return ENOEXEC for that vcpu.
 
+The initial values are defined as:
+	- Processor state:
+		* AArch64: EL1h, D, A, I and F bits set. All other bits
+		  are cleared.
+		* AArch32: SVC, A, I and F bits set. All other bits are
+		  cleared.
+	- General Purpose registers, including PC and SP: set to 0
+	- FPSIMD/NEON registers: set to 0
+	- SVE registers: set to 0
+	- System registers: Reset to their architecturally defined
+	  values as for a warm reset to EL1 (resp. SVC)
+
 Note that because some registers reflect machine topology, all vcpus
 should be created before this ioctl is invoked.